Parietal lesions in humans and monkeys suggest that the parietal lobe can represent many kinds of perceptual information. The proposed experiments are designed to isolate neuronal activity which is intimately involved in perception. We intend to use stimuli that can convey the perception of motion in either one of two directions. These bistable stimuli offer the power of eliciting separate perceptual experiences from the same exact visual stimulus to the retina. Our studies will focus on the parietal stream of the primate brain, long known to be motion sensitive. Analogous studies on the temporal stream have suggested that higher areas in the primate cortex offer departures from exact representations of the visual stimulus. In the dorsal stream, very little is known about the nature of perceptual modulation. Monkeys will be trained to report the perceived direction of motion when presented with either moving dots or gratings. Occasionally, the direction of motion will be ambiguous, that is, the direction can be perceived as one of two directions. We will record from single units in parietal stream areas while the monkey reports the direction of motion. In the case where the direction is totally ambiguous, we will analyze the activity of direction selective neurons to see if the responses are modulated by the monkeys perception (as indicated by his report).